The present invention relates to the manufacture of syringes. More particularly this invention concerns an apparatus for fitting a tip or needle cap to a syringe subassembly formed by a syringe body carrying a needle.
In the production of a syringe the needle or cannula is typically mounted by gluing to the end of a stepped tubular syringe body normally made of glass or plastic. Then a tip cap is fitted over the needle end of the body to preserve sterility of the needle and protect users from its sharp point. The tip cap is formed normally as a tapered sleeve centered on an axis and having a small-diameter closed end and a large-diameter open end from which a rim projects radially. It is made of a stiff elastomer so that it can be force-fitted over the needle end of the syringe body.
The automatic machine that fits the tip cap to the syringe subassembly comprised of the syringe body and its needle typically comprises a holder that supports the syringe subassembly and a system for feeding the caps, open end first, axially over the needle end of the syringe subassembly. The feed system typically comprises a tubular guide whose outer end is connected to a supply of the tip caps and whose inner end opens coaxially with the syringe in the holder.
The problem with such an arrangement is that the cap is normally not centered in the guide tube, instead lying against one of its walls. In fact the cap, whose upper end is quite small, normally is canted inside this guide tube. If the needle tip catches on the inner surface of such a nonstraight cap when it is fitted thereover, it will pierce through it. This will of course impair the sterility of the finished assembly and leave the needle tip exposed which presents a hazard to personnel handling the syringe. In addition the needle often excises and holds a tiny plug of the cap when it catches on it, even if it comes free and does not pierce through it, and during subsequent use this plug of the end-cap material can actually be injected into a patient. The result is therefore a defective or dangerous syringe.
It is therefore an object of the present invention to provide an improved apparatus for fitting a tip cap to a syringe subassembly.
Another object is the provision of such an improved apparatus for fitting a tip cap to a syringe subassembly which overcomes the above-given disadvantages, that is which ensures that the caps are fitted coaxially over the end of the needle subassembly.
An apparatus for mounting a tip cap having a maximum diameter over a syringe subassembly having a syringe body with an end carrying a needle has according to the invention a holder holding the subassembly with the needle substantially on an axis and a tubular guide having a feed passage generally centered on the axis adjacent the holder, of an inside diameter greater than the maximum tip-cap diameter, and open toward the holder. A stop can move between a blocking position between the guide and the holder and an unblocking position offset therefrom. The tip cap is fed through the passage to a position arrested on the stop in the blocking position thereof. A nozzle opening into the passage injects pressurized gas into the passage and thereby spins the tip cap in the passage about the axis. The stop can then be moved from the blocking into the unblocking position for displacing the spinning tip cap from the guide onto the syringe subassembly in the holder.
Thus with this system the tip cap is centered in the passage by the gas, normally compressed air. According to the invention the nozzle opens tangentially into the passage. This imparts excellent spin to the tip cap so that when the stop is withdrawn and, if necessary, the holder and guide are axially moved toward each other, it fits coaxially over the needle onto the syringe body. Thereafter standard devices are used to press the tip cap snugly into place on the syringe body.
In accordance with the invention for most effective spinning two such nozzles open tangentially into the passage diametrally offset from each other.
The stop according to the invention is a plate movable transversely of the axis. It forms a slot at the axis. This plate can have a pair of oppositely movable parts together forming the slot. Alternately the stop is an iris, like a camera shutter. In another system the stop is at least one plate pivotal about an axis lying in a plane perpendicular to the axis between the blocking and unblocking positions.
The passage according to the invention is cylindrical and the axis is upright.